As the Internet has grown in popularity and mobile Internet for text-based information and picture messaging is already a reality, the industry has turned its focus on engineering the most cost efficient network for more demanding multimedia services. IP-based networks are considered by many the best way forward and networking technology research and development is by and large centered around IP-technologies.
The development of an IP-based radio access network will bring together a number of radio access network technologies including second generation (2G), third generation (3G) and Wireless Local Area Networks (WLANs). Network operators are shifting from a circuit-switched to a packet-switched technology, while IP-based networks need to expand radio access rapidly, flexibly and cost efficiently.
IP-based radio access networks can be introduced as a smooth evolution from existing GSM (Global System for Mobile communications), EDGE (Enhanced Data Rates for GSM Evolution) and WCDMA (Wideband Code Division Multiple Access) networks, Key benefits of such IP-based radio access networks are distributed architecture with a separation of user and control planes (offering infinite scalability and no bottlenecks), integration of different radio interface technologies into a single radio access network, common radio resource management for optimum use of radio resources, quality of service (QoS) control, and network automation, open interfaces for multi-vendor networks, and compatibility to existing transmission networks.
In order to obtain the most efficient radio access network architecture, some functionality is suggested to be relocated between network elements. The IP-based radio access network (IP RAN) architecture introduces large radio access network gateways between the radio access network and the core Network. In IP RAN, the functions of UTRAN's Radio Network Controller (RNC) is distributed to other entities of the network. The macrodiversity combiners are no longer located in the RNCs. Meanwhile the macrodiversity combining is located in IP base transceiver stations (IP BTS) in the IP RAN. Also the radio resource control (RRC) is managed in the IP BTSs. In other words, some radio network controller functionality is located in the base transceiver stations to enable soft handover and associated signaling to happen along the shortest path, producing minimum delay and signaling load to those parts of the networks where this is not necessary.
However, current relocation scenarios are designed for radio resource control located in radio network controller (RNC) elements which supervise numerous base transceiver stations (BTSs). When RRC is moved down to the base transceiver station level, the relocation procedure will become much more frequent because the number of BTSs is much greater than the RNCs.
Hence, in order to maintain network performance, some limitations of the current relocation procedure must be removed. In particular, the current RNC-based soft handover, as defined in the 3GPP (Third Generation Partnership Project) specification TR 25.832 (Release '99), is allowed only when the radio link of the source RNC is removed. The relocation phase, which corresponds to a change of the instance for interconnection between a radio resource control network element and a core network or an access gateway of a radio access network, is only supported where all radio links are in a single Drift Radio Network Subsystem (DRNS) and where the Drift Radio Network Controller (DRNC) is the target RNC. In general, relocation procedures are the same for both cases involving the core network and involving the RAN access server.
Thus, multiple D-RNCs or D-BTSs can be established only after the relocation has taken place, and the radio performance cannot be optimized when RRC is moved down to a “lower” network level (e.g. BTS level),